Rapid, highly sensitive, quantitative, non-radioactive assays for estradiol are needed in order to evaluate the physiological roles of low levels of estrogens and to determine the effects of anti-estrogen therapy or dietary phytoestrogens. Detection limits for commercial radioimmunoassays are 2-10 pg/mL, whereas research using cell-based bioassays suggests estrogen levels associated with antiestrogen chemotherapy or precocious puberty are 10-100 fold below that level. Gene Transcription Technologies' goal is to develop and commercialize a yeast-based bioassay with detection limits of less than 0.1 pg/mL. We hypothesize that innovative strain construction which combines an estrogen responsive fluorescent reporter with incorporation of mammalian coactivator genes and yeast transporter mutants will enable development of a non-radioactive estradiol assay in 96 well format. This cell-based bioassay has sensitivity of less than 0.1 pg/mL, cross-reactivity of less than 1 percent for estrogen metabolites and antiestrogens, and a correlation coefficient of greater than 0.85 with standard RIA at estradiol levels greater than 2 pg/mL. PROPOSED COMMERCIAL APPLICATION: Clinical laboratories, research scientists, environmental organization and clinicians are in need of an ultra sensitive assay for estrogen. The most sensitive method, currently available use radioactivity, and are not as sensitive as the technology being developed by GTT. The new assay will not only have applications in clinical settings but it will also be useful in drug discovery, toxicology, and detection of endocrine disrupters in food and environment. The market for estrogen assays of approximately 2 pg/mL sensitivity is on the order of 120 million dollars/year.